Radio direction finder



Oct. 4, 1949.

RECEIVER IIII G. S. BURROUGHS RADIO DIRECTION FINDER Filed April 9, 1946 ATTORNEY- Patented Oct. 4, 1949 I UNITED STATES PATE NT oFFic-E' RADIO DIRECTION FINDER Gordon S. Burroughs, Forest Hills, N. Y., assignor to Federal Telecommunication Laboratories, Inc., New York, N. Y., a corporation of Delaware Application April 9, 1946, Serial No; 660,613

a scam.

My invention relates to phase comparison system, and more particularly one for use in radio direction finders.

It is known that the cathode ray tube can be used in various circuit connections to indicate instantaneously phase relationships between voltages and currents by a more Or less sharp trace line on the screen, which by its angular position respecting a reference point indicates a phase displacement. This angularindication however, will not be accurate unless certain very exacting re-- quirements respecting balancing facto'rs such as phase and amplitude of the respective voltages.

applied to the deflector circuits, be complied with.

A further disadvantage of these known devices arises from the fact that inaccuracies due to the aforesaid causes will occur unnoticed. Thesedisadvantages become ofconsiderable importance when a phase indicator of the-type mentioned is used in connection withdirect-reading directionfinders.

It is an object of my invention to provide a phase comparison indicating arrangement wherein an existing phase displacement between two voltages is accurately indicated-notwithstanding variation in the transmission characteristicswof the translating means between the voltages COB-1 cerned and the indicator. 5

Another object of myinvention I a phase comparison system utilizing .a cathode is provide ray tube as the phase indicator andwhereinlthe screen trace substantially accurately indicates phase angle even thoughzthetrace shape -mayundergo a change. VI

A further object of mydhvention is to provide 3 a radio direction finder,'"utilizing a phase com parison of the type aboveindicated in which 'one oi the voltages is produced by the efieotive rota:

tion of a directive radiation patterm asifqi ex-" ample, through a gonioineter, and the other voltage is a reference voltageproducedinfsynchro nism with the goniometer operationfi 7 A still further object may invention isto provide a radio direction finder in which goniom eter action produces two voltageswhose fdisplace': ment in phase varies with the an-gular changein the directive radiation "pattern; together with means for translating this displacement'into'sub; stantially linear indication on a cathode j ray tube screen.

sun another object 'ormyinvenuonis a pro-.1 1

vide a direction finder of the typeindicated'inthe last preceding paragraph in which derivations of both the voltages are applied to both of the deprincipal voltages in the circuits of Fig. 1.

The particular directional antenna chosen for:

illustration comprises two right-angle loops J and 2 connected, respectively, tothe two' p'airs 0pmmary windings'3 and 4 of aconventional 'goniometerf The secondary pick-up coil 5, carried on the shaft 6 of the motor I, is rotatably mounted in inductive relation with the primary windings so that l as the pickup coil rotates, the coil ter-, minal voltage varies in the same manner as'would.

the terminal voltage of a rotating loop'in the same" field. A single rotating loop may it desired be substituted for the goniometer and crossed'loops.

The directional antenna is connected to'the input ofa reciver 8 containing theusualdetecting' circuits which will deliver to"the'receiver'output a direct current voltage proportional to the applied antenna voltage. The, receiver, output will .lvary cyclically at the speed of. the motor driven coil when a radio wave is received by the antenna, and the time phase of the cycliclvariations will change i as the azimuthal direction of-lthereceived wave changes. To remove the ambiguity of th two a degree indications at the terminals of the rotat mg goniometer, caused by the',cardioid; pattern of the loops the usual pmni-directionalvertical antenna 9 is inductively coupled legs" of the'loop circuit.

Accordingto animportan feature of Qmy-in vention, an alternating game s generator lor al A tematori iisdriven by themotor; the frequency of the alternatingjoutputvvoltage. being equal top the periodicity of the j .receiverjjoutput. v With a two-pole valternator,"direct FQUDling to the alternator and to thefgonio meter pick-up coil, will give the necessary matched frequencies. a

. 'lhe relativetimephasesofgthegeneratedalternatin'givoltage and thereceiver output'voltagerare 1 determined by the directionoithe receivediwave;

and according to another feature of my invention, nove1 means are provided for comparing and vis- "at lilf to'thetwo ually indicating the phase of these voltages in terms of direction.

The cathode ray tube I2 is preferred as the indicating device, the pairs of deflection plates it, Hi and l5, l6 being so coupled to the voltages to be compared that a straight light line II, as shown diagonally across-the screen, will pivot about the center point of the screen in response to changes in direction of the received radio wave. A scale of 360 degrees may be laid out about the periphery of the screen. For convenience of description, plates I3 and I 4 will be arbitrarily referred to as vertical deflection plates, and plates I5 and I6 will be called horizontal deflection plates. Magnetic beam deflectors could be substituted.

The alternator voltage is applied to a transformer l8, the secondary winding of which is tapped at its center l9, thus providing two windings and 2| with phase opposed voltages, and the receiver output voltage is applied to a transformer 22, of which the secondary winding 23 is connected at one end to said center tap l 9. Windings 20 and 23 are thus connected in series and to the vertical deflection plates l3 and I4, while windings 2| and 23 are connected in series and to the horizontal deflection plates l5 and 16. In the latter connection, a phase shifter 24 is included. The particular phase shifter shown is adjustable over a 0-to-180 degree range and comprises resistor 25 and capacitor 26, the relative values of which are selected to give a 90 degree shift. Fine adjustment of the shifter may be obtained by an additional resistance and condenser in parallel thereto. In order to compensate the I attenuating effect of the phase shifter an attenuator 21 is used in the vertical deflecting circuit.

The operation of the coupling circuits of Fig. 1 may best be considered with a vector diagram of the important voltages, such as shown in Fig. 2. Assume that the pick-up coil 5 and the rotor of the alternator H are so oriented on the motor shaft that the alternator voltage and the receiver output voltage are in phase when a received signal arrives from due north. Then if a radio wave is received at an angle 0 with the north-south meridian, the phase angle of the receiver output voltage Ea with respect to the alternator voltage E1 will be 0. Voltages E1 and E2, of the two halves of the divided winding are, of course, 180 degrees out of phase. The vectorial sum, of 0E1 and 0E3 shown in Fig. 2, is voltage 0V which is applied across the vertical deflection plates l3 and M. The vectorial sum of OR: and CE: is voltage 0H which upon being shifted 90 degrees by the phase shifter 24 to position OH is applied to the horizontal deflection plates l5 and I6.

Since voltage 0V on the vertical deflection plates is in phase with voltage OH on the horizontal deflection plates, a straight line on the screen can be produced, the angle of the line being a'function of the angle 0 which the voltage 0E3 makes with voltage 0E1 and 0E2.

Additionally, it is possible to view the operation'analogously to that in patent to Busignies et al., 2,263,377, Nov. 18, 1941, where two oppositely rotating vectors under given conditions may eiiect a linear phase indication on a cathode ray oscillograph screen. In the instant case the generator and receiver voltage vectors existing in the circuits described produce such an effect, and it will be linear under conditions described including equality of amplitude. If amplitudes are different the locus of resultant points will be on 4. an ellipse, whose major axis corresponds to linear indication for equal amplitudes.

A straight line on the screen requires that E:

equal E1 or E2, a condition which can be approximated with manual gain controls and automatic volume controls in the receiver. If these two voltages should become unequal, the line on the screen becomes an elongated ellipse, but with the major axis still pointing inv the proper direction, and the observer is correctly apprised of the facts such as unequality of voltages. Hence, for a given wave received by the antenna, the frequency and phase of the voltages to be compared are fixed by the keyed connections of the pick-up coil 6 and alternator H to the motor shaft and any amplitude variations are clearly shown on the screen and are rendered harmless.

the screen of my novel direction indicator.

My improved direction finder is mechanically simple, easy to operate, and most important, is reliable.

While I have described in some detail an embodiment of my invention, it is to be understood that this is only by way of explanation and not limitation and that various changes are possible without departing from the spirit and scope of my invention.

I claim:

1. A radio direction finder comprising a first source of alternating voltage, a second source producing a single phase alternating voltage, the phase relation of the voltages of the two mentioned sources being variable in response to varying directions of a received radio wave; means for comparing and visually indicating said phase relation comprising a cathode ray tube with right-angle beam deflectors, means to combine said first and second voltages to obtain separate vector sum and difference voltage components thereof, connections to apply one component to one beam deflector, a 90 degree phase shifter, and connections to apply the other component through said phase shifter to the remaining beam deflector.

2. A radio direction finder comprising two alternating voltage sources, a transformer with 'a center-tapped secondary winding, one alternating voltage source coupled across said winding, connections for applying the other alternating voltage to the center tap of said secondary winding to obtain separate vector sum and difference voltage components of said two voltages, a phase shifter for shifting the phase of one of said components, and means for comparing the other component with the phase shifted component.

3. A radio direction finder comprising an antenna having an asymmetrical direction pattern, a motor, means driven by said motor for deriving a voltage cyclically variable at the speed of said motor and in phase with the signal strength at the terminals of said antenna corresponding to a continuously varying direction about said antenna, an alternating current generator connected to said motor, and means comparing the 76 4. A direction finder comprising a cathode ray 7 phase of the cyclically variable voltage with the phase of the alternating output of said generator comprising means for combining said variable voltage with the output of said generator to obtain separate vector sum and difference voltage components thereof, means for shifting the phase of one of said components and means for comparing said other component with said phase s-hifted component.

All misleading information is thus effectively eliminated from tube having two right-angle beam deflectors, two transformers, the secondary winding of one of said transformers having and terminals and a. tap terminal connected to the center of said winding, the secondary winding of the other transformer being connected between the mentioned tap terminal and a common terminal for said two rightangle beam deflectors, the remaining terminals of said two deflectors being connected, respectively, to said end terminals and means for shifting 90 electrical degrees the voltage applied to one of said remaining terminals.

5, In direction finders, a radio goniometer, an alternator, a motor mechanically coupled to said oniometer and to said alternator, and a radio receiver electrically coupled to said goniometer; a cathode ray tube having two pairs or beam deflection plates, a first and a second transformer winding, coupled, respectively, to said alternator and to the output of said radio receiver, said first winding having a center tap, a phase shifting device, two contiguous deflection plates of the tube being connected together and to one terminal of said second winding the other 6 terminal being connected to said center tap, the remaining deflectionplates being connected, respectively, to the end terminals of said first winding, said phase shifter being connected in circuit with one of the last mentioned connections.

GORDON S. BURROUGHS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,166,991 Guanella July 25, 1939 2,223,840 Wolfi Dec. 3, 1940 2,281,995 Purington May 5, 1942 2,314,851 Barney et a1 Mar. 23, 1943 2,328,985 Luck Sept. 7, 1943 2,374,817 Hardy May 1, 1945 2,388,262 Ganiayre Nov. 6, 1945 2,406,800 Busignies Sept. 3, 1946 2,408,039 Busignies Sept. 24, 1946 2,408,120 Wirkler Sept. 24, 1946 

